MR elements including various magnetic sensors (MR sensors) and magnetic heads (MR heads) are to detect a change in electric resistance produced in a magnetic film on application of a magnetic field to thereby measure the magnetic field intensity or its change. They are generally required to have a great differential magnetoresistance and a low operating magnetic field intensity at room temperature.
Prior art MR elements used magnetic films of Fe-Ni (Permalloy) and Ni-Co alloys in order to take advantage of their anisotropic magnetoresistance effect. The Fe-Ni and Ni-Co alloys can operate with a low magnetic field intensity, but have a differential magnetoresistance as low as 2 to 5%.
With the advance of the modern thin film technology, artificial superlattices were developed using a molecular beam epitaxial (MBE) method. Each artificial superlattice has a multilayered structure including thin metal layers having a thickness of an atomic order stacked at regular intervals using a molecular beam epitaxial (MBE) method and exhibits different properties from bulk metal.
One of recently developed artificial superlattices is a giant magnetoresistance changing material in the form of an Fe/Cr magnetic multilayer comprising alternately stacked Fe and Cr films. In this multilayer, a pair of Fe films sandwiching a Cr film are magnetically coupled in antiparallelism. On application of an external magnetic field, Fe spins are gradually aligned in one given direction and accordingly, the resistance lowers. As a consequence, the multilayer shows a giant magnetoresistance change of 46% at 4.2K and 16% at room temperature (see Physical Review Letters, Vol. 61, page 2472, 1988). The Fe/Cr magnetic multilayer has such a giant magnetoresistance change, but requires an operating magnetic field intensity of about 20 kOe, which imposes some limitations on the multilayer in practical use.
Active research efforts were concentrated on the artificial lattice magnetic multilayers exhibiting antiferromagnetism. Up to the present, interlaminar coupling of antiferromagnetic spins was discovered in Co/Cr and Co/Ru magnetic multilayers (see Physical Review Letters, Vol. 64, page 2304, 1990). The magnetoresistance change is undesirably as low as 6.5% at 4.5K for the Co/Cr system and 6.5% at 4.5K for the Co/Ru system.